I don't know if you use some sort of safety treadmill but on many, you will fall if you don't/can't run anymore. There's your metaphor for life. Also, running on a treadmill is/can be viewed an image for not moving forward despite all the running you do.
Yeah, I thought the treadmill image was about having to keep running just to stay in the same place (a Red Queen’s race) rather than anything about falling down.
